1. Field of the Invention
This invention pertains generally to high-contrast gratings, and more particularly to enhanced reflectivity in sub-wavelength high-contrast gratings (HCGs).
2. Description of Related Art
Subwavelength high-contrast gratings, having a high refractive index material surrounded by low index material, have been shown to be extremely effective as a highly reflective, broadband mirror with many beneficial properties. A single layer of HCG proves to be as good a mirror as a 40-layer distributed Bragg reflector (DBR). Application can be made of these devices in numerous applications, such as within VCSELs to replace the top DBR mirror while selecting a preferred lasing polarization. The inventors have shown these devices also can provide a high-Q resonator, for mirror sidewalls of a hollow waveguide, and are particularly well-suited for MEMS-based applications because of their small size.
Despite the numerous advantages of HCG, further benefits could be derived by improving their responses, such as increasing reflectivity. In addition, the necessity of surrounding the HCG with low refractive index materials in certain applications is problematic. For example, the bottom mirror of a VCSEL is typically embedded within relatively high refractive index semiconducting materials, due to electrical and thermal conductivity considerations.
Accordingly, improving HCG mirror characteristics would benefit numerous applications. The present invention teaches inventive embodiments which increase the reflectivity of subwavelength high-contrast gratings, and allow integration of HCG reflectors in a wider range of applications.